software/seleniumserver: add a promise to wait for all nodes to register

We are sometimes seeing test failures when nodes can not register before the
beginning of the test, this promise make sure the grid is ready to use.

software/seleniumserver/buildout.hash.cfg

@@ -19,4 +19,4 @@ md5sum = c4ac5de141ae6a64848309af03e51d88
 
 [template-selenium]
 filename = instance-selenium.cfg.in
-md5sum = fc2e8176929063903a69b0e80007ca63
+md5sum = eea51d25c292c7ea305229184e380814

software/seleniumserver/instance-selenium.cfg.in

@@ -66,6 +66,7 @@ port = 4444
 base-url = http://$${:hostname}:$${:port}
 url = $${:base-url}/wd/hub
 register-url = $${:base-url}/grid/register/
+api-url = $${:base-url}/grid/api/hub
 
 
 [selenium-server-node-instance]
@@ -259,6 +260,7 @@ instance-promises =
   $${sshd-listen-promise:name}
   $${selenium-server-frontend-listen-promise:name}
   $${selenium-server-hub-listen-promise:name}
+  $${selenium-server-hub-nodes-registered-promise:name}
   $${selenium-server-node-firefox-52-listen-promise:name}
   $${selenium-server-node-firefox-60-listen-promise:name}
   $${selenium-server-node-firefox-68-listen-promise:name}
@@ -285,6 +287,30 @@ config-port = $${selenium-server-frontend-instance:port}
 config-hostname = $${selenium-server-hub-instance:hostname}
 config-port = $${selenium-server-hub-instance:port}
 
+# Promise waiting for all nodes to be registered
+[selenium-server-hub-nodes-registered-promise]
+<= monitor-promise-base
+module = check_command_execute
+name = $${:_buildout_section_name_}.py
+config-command =
+  $${selenium-server-check-nodes-registered:rendered} $${selenium-server-hub-instance:api-url} $${:expected-node-count}
+# We have 4 nodes with 3 slots each
+expected-node-count = 12
+
+[selenium-server-check-nodes-registered]
+recipe = slapos.recipe.template:jinja2
+rendered = $${directory:bin}/$${:_buildout_section_name_}
+mode = 0755
+template =
+  inline:
+  #!${buildout:executable}
+  import json, urllib, sys
+  api_url = sys.argv[1]
+  expected_node_count = int(sys.argv[2])
+  actual_node_count = json.load(urllib.urlopen(api_url))['slotCounts']['total']
+  sys.exit(0 if expected_node_count == actual_node_count else 1)
+
+
 [selenium-server-node-firefox-52-listen-promise]
 <= check-port-listening-promise
 config-hostname = $${selenium-server-node-instance-firefox-52:hostname}